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147 1.9 16V - Overboost

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overboost
911 views 3 replies 3 participants last post by  tishobg 
#1 · (Edited)
After a casual diagnostic, my mechanic noticed my car was overboosting by about 0.4-5 bar . Either a VGT Solenoid or vacuum hoses in my opinion, his money are on the solenoid.
These vacuum hoses though, I'm interested can I inspect them myself with out disassembling a lot of stuff? Mechanic is off work for a few weeks and I trust only him. I hope it's them, since they have never been changed. Just cheaper to replace than a solenoid.. Any pointers where to look for them ,much appreciated. If not those two, what else could be causing it? EGR - cleaned. Decat, straight pipe.
P.S. A problem with the geometry shouldn't be a possibility, since it'll usually keep the car less powerful if they're blocked and the turbo needs cleaning,am I right? My car definitely doesn't go slow, it can eat it's tires even in 3rd.
P.S.2 Is the so called solenoid a piece that can actually be cleaned ,instead of replaced with new?
 
#2 ·
Sticky VNT mechanism can definitely cause issues...

The Vac system pulls the VNT in to high-boost position, then releases it to return to lower boost positions... Normally cracks/splits in the vac lines mean you can't pull sufficient vacuum in the actuator so never actually get to high boost and the car feels sluggish and lacking power...

There's a small air filter on the VNT solenoid that releases the vacuum to the actuator... If this is blocked you might find that the turbo sticks in high boost for longer than it ought to...

Locate the turbo, and then follow the small diameter hoses coming off of the actuator... All tucked in the front between the radiator and the engine block.. Simple as that! You might have to pop the solenoid valve off to properly get to the air filter... If you're disconnecting hoses be very careful! The small plastic barbs on the solenoid get brittle over time and are easy to snap off if you're not careful... Meaning you can either glue t back together, or replace it with a new one.

Do you have a remap? Might be getting issues compounded by running a straight-pipe turbo back exhaust... Not cat providing resistance will make it that much easier for the turbo to boost up harder...
 
#3 ·
How was over boost diagnosed? If the car pulls well and no engine light illuminates then you have no problems and no fix is required. Half a bar of boost extra is a lot! If your car is making this with out going into limp then it has probably had a remap.
With regard to the vnt hoses. Change them as it is so cheap and easy to do. However, lack of vacuum causes under boost not overboost.
 
#4 · (Edited)
Car pulls extremely well.I've driven a 180HP 147 and honestly, it didn't feel much faster.
I've gotten only one MSFC error but after I cleaned the EGR, absolutely nothing and I floor my car in a daily basis.My mechanic just said he noticed it overboosting, but apparently no errors are recorded in the ECU. Does that sound like a remap? I've wanted to do it, but if my car already has it, i'd be real happy. Maybe i'll take it to the local tuner and he can check and maybe tune it properly so that tie air/fuel ratio is even.

Sticky VNT mechanism can definitely cause issues...

The Vac system pulls the VNT in to high-boost position, then releases it to return to lower boost positions... Normally cracks/splits in the vac lines mean you can't pull sufficient vacuum in the actuator so never actually get to high boost and the car feels sluggish and lacking power...

There's a small air filter on the VNT solenoid that releases the vacuum to the actuator... If this is blocked you might find that the turbo sticks in high boost for longer than it ought to...

Locate the turbo, and then follow the small diameter hoses coming off of the actuator... All tucked in the front between the radiator and the engine block.. Simple as that! You might have to pop the solenoid valve off to properly get to the air filter... If you're disconnecting hoses be very careful! The small plastic barbs on the solenoid get brittle over time and are easy to snap off if you're not careful... Meaning you can either glue t back together, or replace it with a new one.

Do you have a remap? Might be getting issues compounded by running a straight-pipe turbo back exhaust... Not cat providing resistance will make it that much easier for the turbo to boost up harder...
I'll check those today, thanks. I've considered the straight pipe as a culprit as well. It's an entirely free flowing exhaust, straight from the turbo to the back of the car. The sound is makes is mighty.

It's all very weird, I'd expect on MSFC error if the car was that overboosting. I've recently taken it for a top speed run and drove it flat out for 3-4KM's , with a slight incline, around 180-200km/h speed. No error.
 
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